Mortality/Probit Calculator

The Mortality/Probit Calculator is a vital tool within RISKCURVES for estimating the fraction of mortality resulting from exposure to toxic chemical concentrations. It also supports unit conversions between three different dose units, making it a versatile instrument for risk assessments and consequence analysis. This article provides a comprehensive guide on how to use the Mortality/Probit Calculator effectively.

Purpose of the Mortality/Probit Calculator

The primary function of the Mortality/Probit Calculator is to estimate the potential lethality of chemical exposures by converting exposure concentrations and durations into mortality probabilities using Probit functions. This tool aids in performing detailed risk assessments and consequence modelling.

Using the Mortality/Probit Calculator

• Navigate to the calculator: Access the Mortality/Probit Calculator from the "Tools" tab in the RISKCURVES Menu bar by selecting "Mortality/Probit Calculator" from the dropdown list.

• Input data: Input the necessary data for your analysis, which includes:

  • Chemical substance: Choose the chemical substance for which you want to calculate the mortality rate.

  • Exposure concentration: Enter the concentration of the chemical exposure.

  • Exposure duration: Specify the duration of the exposure.

• Result collection:

  • The mortality fraction is specified in the calculator.

  • Alternatively, the user could try finding out what would be the concentration required to reach a mortality of 1% (or another given value) for the introduced exposure duration.

Unit conversion

The Mortality/Probit Calculator presents the dose value for each of the three commonly used units for concentration:

• kg/m³

• mg/m³

• ppm

To convert between units, right-click on the unit of the probit, concentration, or exposure duration. This will display other possible units and convert the currently displayed value accordingly. This feature ensures flexibility and ease of use when working with different measurement systems.

Example calculation

Example 1: Exposure times

The Mortality/Probit calculator and lethality contours work together to provide detailed insights into chemical toxicity at various concentrations and exposure durations.

For example, the 1% lethality concentration contour represents the maximum hazard distance reached by a concentration causing 1% mortality at a given exposure duration. It is important to note that this does not mean the concentration is constantly present at that distance for the entire exposure duration.

Users can adjust exposure time in the calculator to assess its impact on mortality. For instance, shorter exposure durations may lead to different mortality percentages, as shown in the animation below.

Example 2: Compare toxicity

The Mortality/Probit Calculator can also compare the toxicity of different chemicals at the same concentration levels.

By inputting the same concentration levels for two chemicals, users can quickly assess their relative toxicity. This helps in understanding the results from the toxic dispersion model and in making informed decisions about chemical safety. The picture below, compares the toxicity of three chemicals which reveals surprising differences in lethality.

Conclusion

The Mortality/Probit Calculator is an essential tool for estimating the potential lethality of chemical exposures in RISKCURVES. By converting exposure concentrations and durations into mortality probabilities, it aids in performing detailed and accurate risk assessments and consequence analyses. This tool enhances the ability to make informed decisions regarding safety and risk management in industrial settings.